My desktop wallpaper today is a second shot from this week’s theme … a Japanese katana.
In this closer shot, you can see the martensite crystals that form the hamon line, which in Japanese are known as nioi. You can also see the distinctive turnback on this particular blade, where the hamon line turns back on itself for a short distance, just before the blade meets the guard (tsuba in Japanese). I’m told that sword appraisal books don’t mention turnback features like this one, so it may be aesthetically interesting but not considered notable.
You can also see the wear and tear on the blade from hundreds of years of cleaning, especially some of the larger scratches. This blade is believed to date from the Koto period, which ended in 1596 (although putting a date on it is a gross over-simplification, as with all things to do with the appreciation of the katana). It must be properly oiled after every use to keep the iron sealed against contaminants that would cause it to rust.